Free memory in Watson Knowledge Studio

I had to deploy a model in both our dev space and prod space in bluemix using Watson Knowledge Studio. I created a first model snapshot for the dev space and it worked. I created a second snapshot for our prod space and I got the error: This operation cannot be completed because the model size exceeds the subscription storage size 10 GB.

I deleted previous models and projects but it didn't change anything. Then I deleted the dev snapshot I just did and tried again, but now I can't even recreate my dev snapshop. They might be doing a "soft delete" instead of a "hard delete" so anything I delete does not free any memory. We don't want to upgrade now as we have a lot of tasks in progress. How can I free memory to deploy my new model?